The Secret Diary of Laura Palmer is a 1990 spin-off novel from the television series Twin Peaks by Jennifer Lynch.Lynch, then aged 22, is the daughter of series co-creator David Lynch. It was published between the airing of the first and second season.

The novel is said to be "As seen by Jennifer Lynch," and is written in a matter-of-fact tone from the point of view of Laura Palmer, a small-town teenager —a "good girl gone bad"— who is abused and terrorized by the demonic entity BOB. Lynch says she was told by her father and Mark Frost, co-creator of the series, to "be Laura Palmer," and that she "knew Laura so well it was like automatic writing. The book begins on Laura's 12th birthday in 1984, and steadily matures in writing style and vocabulary. It recounts standard teenage concerns of her first period, her first kiss, and her relationship with her parents, alongside experiences of sexual abuse, promiscuity, cocaine addiction, and her obsession with death. Laura's poetry foreshadows her murder. Her slow realisation of BOB's identity is described, although pages are 'missing' from the end of the diary, which ends with an undated entry in late 1989, leaving the reader unable to reach a firm conclusion. Lynch said that "the careful reader will know the clues and who the killer is," and the killer's identity is confirmed in the second season.

The book reached number four on The New York Times paperback fiction best seller list in October 1990, though some US book stores refused to stock it due to the graphic content. It was published in the UK by Penguin Books in November 1990. Entertainment Weekly said it was "gratifyingly faithful to the spirit of Peaks."

On June 10, 2011, Twin Peaks co-creator Mark Frost announced that a new edition of the diary would be published in the fall of 2011, featuring a new foreword by himself and David Lynch.

An audiobook, narrated by Sheryl Lee, was released in May 2017